Photochemical reactivity of substituted phenacyl chromophores

Bc. Lukáš Plíštil

Master's thesis

Abstract:

Photoenolization reaction of ortho-alkyl substituted phenacyl derivatives can be used for preparation of new indan-1-ones. The photolysis of 2-(methoxymethyl)-5-methylphenacyl chloride in nonpolar solvents leads to a formation of the corresponding indan-1-one in low yields, whereas the major product is 3,5-dimethyl-2-benzofuranone. The topic of my diploma thesis was the investigation of the reaction mechanism for this reaction sequence. 2-(Methoxymethyl)-5-methylphenacyl chloride reacts in a photoenolization fashion to form photoenols being attacked by a molecule of water. The product of this process, 2-hydroxy-2-(methoxymethyl)-5-methylacetophenone, then hydrolyses to 2-acetyl-4-methylbenzaldehyde. This species undergoes another photoenolization resulting in the formation of 3,5-dimethyl-2-benzofuranone. Water is a key reagent in this process, the reaction pathway leading to 3,5-dimethyl-2-benzofuranone is completely suppressed under dry conditions, while only corresponding indan-1-one is formed. The investigation of the transients involved in the reaction sequence was performed by the laser flash photolysis together with a quenching study. The results obtained showed that the formation of 2-acetyl-4-methylbenzaldehyde proceeded predominantly via the singlet state to form Z-photoenol. Its lifetime was found to be unusually long compared to the published results. This observation can be explained by the formation of intramolecular hydrogen bond in the case of ZZ-photoenol. This assumption was supported by the quantum chemical calculations of similar structures. The formation of 2-acetyl-4-methylbenzaldehyde in acetonitrile proceeded via the triplet state to form long-lived E-photoenol, while the Z-photoenol is a short-lived species that reketonize back to the starting material. LFP of 2-acetyl-4-methylbenzaldehyde showed the formation of two transients, which were assigned to Z- and E-ketenols. Z-ketenol formed via the singlet state is the transient responsible for the formation of 3,5-dimethyl-2-benzofuranon, while E-ketenol reacts back to the starting material.

Kľúčové slová

Photoenolisation, phenacyl chromophore

Jazyk práce: Czech

Datum vytvoření / odevzdání či podání práce: 3. 5. 2006

Obhajoba závěrečné práce

• Obhajoba proběhla 16. 5. 2006
• Vedúci: prof. RNDr. Petr Klán, Ph.D.

Masaryk University

Faculty of Science

Master programme / odbor:
Chemistry / Organic Chemistry